The present invention relates to a rotary compressor equipped with first and second rotary compressing elements driven by a rotary shaft of a driving element, which are accommodated in a hermetically sealed vessel.
In this type of conventional rotary compressor, especially an internal intermediate pressure multistage compression type rotary compressor, a refrigerant gas is introduced through a suction port of the first rotary compression element into a low-pressure chamber of a cylinder wherein the refrigerant gas is compressed to have an intermediate pressure by a roller and a vane, and then discharged from a high-pressure chamber of the cylinder into the hermetically sealed vessel through the intermediary of a discharge port and a discharge muffling chamber. The refrigerant gas having the intermediate pressure in the hermetically sealed vessel is then drawn into the low-pressure chamber of the cylinder through a suction port of the second rotary compressing element and subjected to second-stage compression by the roller and the vane. This causes the refrigerant gas to turn into a hot, high-pressure refrigerant gas, which flows from the high-pressure chamber into an external radiator or the like through the intermediary of the discharge port and the discharge muffling chamber (refer to, for example, Japanese Patent No. 2507047).
The rotary shaft has an oil bore vertically formed around an axial center thereof and a horizontal lubrication bore in communication with the oil bore. Oil is drawn up from an oil reservoir located at bottom inside the hermetically sealed vessel 12 by an oil pump, serving as a lubricating device, installed at the bottom end of the rotary shaft. The oil moves up through the oil bore to be supplied to the rotary shaft and sliding portions in the rotary compressing elements through the lubrication bore, thereby to accomplish lubrication and sealing.
If a refrigerant exhibiting a considerable high/low pressure difference, such as carbon dioxide (CO2), which is a natural refrigerant, is used in the abovementioned rotary compressor, then the refrigerant pressure reaches 12 MPaG in the second rotary compressing element, which is the high pressure side, while it reaches 8 MPaG (intermediate pressure) in the first rotary compressing element, which is the low pressure side.
In such a rotary compressor, an upper open surface of the cylinder of the second rotary compressing element is closed by a supporting member, and the lower open surface thereof is closed with an intermediate partitioner. A roller is provided in a cylinder of the second rotary compressing element. The roller is fitted to an eccentric member of the rotary shaft. For a design reason or for preventing wear on the roller, a small gap is formed between the roller and the supporting member disposed above the roller, and between the roller and the intermediate partitioner disposed under the roller. These gaps inconveniently allow a high-pressure refrigerant gas, which has been compressed by the cylinder of the second rotary compressing element, to enter into the roller (a space around the eccentric member inside the roller). Thus, the high-pressure refrigerant gas accumulates inside the roller.
The high-pressure refrigerant gas built up inside the roller causes the pressure inside the roller to become higher than the pressure (intermediate pressure) of the hermetically sealed vessel, which has its bottom portion serving as the oil reservoir. This makes it extremely difficult to supply oil to the inside of the roller from the lubrication bore through the oil bore in the rotary shaft by utilizing a pressure difference, resulting in shortage of a lubricant to the area around the eccentric member inside the roller.
As a conventional solution to the abovementioned problem, a passage 200 that provides communication between the inside of the roller (adjacent to the eccentric member) of the second rotary compressing element and the interior of the hermetically sealed vessel has been formed in the upper supporting member 201 disposed above the cylinder of the second rotary compressing element, as shown in FIG. 16. The passage 200 releases the high-pressure refrigerant gas accumulated inside the roller into the hermetically sealed vessel so as to prevent the pressure inside the roller from rising to a high level.
However, to form the passage 200 for the communication between the inside of the roller and the hermetically sealed vessel, two passages have to be formed by machining, namely, a passage 200A formed in an inner edge portion of the upper supporting member 201 in an axial direction that opens adjacently to the inside of the roller, and a horizontal passage 200B for providing communication between the passage 200A and the hermetically sealed vessel. This has been posing a problem of increased machining cost for forming the passages with resultant higher production cost.
Furthermore, the pressure (high pressure) in the cylinder of the second rotary compressing element becomes higher than the pressure (intermediate pressure) in the hermetically sealed vessel having its bottom portion serving as the oil reservoir. This makes it extremely difficult to supply oil through the oil bore and the lubrication bore in the rotary shaft into the cylinder of the second rotary compressing element by utilizing a pressure difference. As a result, lubrication is performed only by the oil in a refrigerant drawn in, thus posing a problem of insufficient lubrication.
Furthermore, in the internal intermediate pressure multistage compression type rotary compressor, the pressure in the cylinder (high pressure) of the second rotary compressing element rises higher than the pressure in the hermetically sealed vessel (intermediate pressure) having its bottom portion serving as the oil reservoir. This makes it extremely difficult to supply oil through the oil bore in the rotary shaft into the cylinder by utilizing a pressure difference. As a result, lubrication is performed only by the oil in a refrigerant drawn in, thus posing a problem of insufficient lubrication.
Thus, the intermediate partitioner and the cylinder of the second rotary compressing element have to be provided with small bores to provide communication between the oil bore of the rotary shaft and the inlet port of the cylinder so as to supply oil to the second rotary compressing element. This, however, has been posing a problem of increased production cost because of the need for forming the small bores in the intermediate partitioner and the cylinder.